[Xen-users] Device Drivers in xen, looking also for a white book about how xen works exactly‏

[Patrick Archibal <bugpb60@xxxxxxxxxxx>]

Hello,
 
I'm reading an excellent documentation about virtualisation in embedded system.
 (available on open kernel labs site)
 
I have read these things : (It talks about managing drivers in a virtualization system)
 
"A straight virtualization approach can accomodate this by running the device the device driver inside the VMM. This requires porting all drivers to the hypervisor environnement , with no reuse of guest os driver"
 
A much better approach is to share a single driver between multiple vms, without including it in the hypervisor. This requires that ecah participating subsytem has a device modem for which it has a device driver. Typically, the real device driver is contained in one of the participating system, but a better  (safer) solution is to separate it out into in own subsystem"
 
I want to know how it works on xen.
I think that :
 
 All drivers are in the hypervisor, when a guest requires to use a device,  guest uses drivers which has been rewriten for xen in order to contact the hypervisor. Then, the hypervisor which has all real drivers (not modified) call the real device ?
 
or that :
The real device driver is contained in the dom0 system, the dom0 manage driver for all domU.
 
I have three questions :
 
1 -  Which is the good scenario ? (if one is good ) :o)
2 - If drivers for guests are rewritten to call hypervisor or dom0 instead of the device directly, who devellops driver ?
(xen devellopers ? or developper for kernel mainline)
3- Which is the real utility of dom0 system ? (just I/O and administration of virtual machines) 
 
Last question, is someone have find a good white paper or doc which explains how xen works ?
(and where i can find probably answers for my questions ??)
 
Thanks for all this details.
Best regards
 
Patrick Archibal

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